1. Field of the Invention
The present invention relates to a radio communication apparatus such as a mobile telephone, portable telephone, cordless telephone, transceiver apparatus, satellite communication apparatus, and the like. More specifically, the present invention relates to a radio communication apparatus used in a radio communication system adopting a time division multiple access (TDMA) transmission method by which radio frequency signals are transmitted between a base station and mobile units in a burst form during one or more time slots.
2. Description of the Related Art
As the number of subscribers in cellular radio systems increase, cellular radio systems have adopted a TDMA transmission method so that signals are transmitted at a more efficient rate. In the TDMA transmission method, signals constitute a continuous sequence of frames. The length of each frame is predetermined. Further, each frame constitutes a plurality of time slots. At least one of the time slots is assigned to a particular mobile unit. The particular mobile unit transmits signals to a base station over radio links during the assigned time slot.
To make TDMA transmission work well, each mobile unit should transmit signals only during its assigned time slot. This operating requirement may, however, be violated if a circuit device of a mobile unit does not operate properly, for instance, due to a large accrued operating time of the circuit device or if there is a strong impact to the device, for example, when the mobile unit is dropped. Transmission in non-assigned time slots due to such a malfunction may cause communication interference between other mobile units and the base station during these non-assigned time slots, that is, when two different mobile units attempt to use the same time slot.